The present invention relates to a copper foil for printed circuit and a copper-clad laminate, and in particular relates to a copper foil for printed circuit and a copper-clad laminate having alkali etching properties as well as favorable thermal peeling strength and thermal oxidation resistance as a result of performing roughening treatment on the surface of the copper foil by way of copper-cobalt-nickel alloy plating and thereafter forming a cobalt-nickel alloy plated layer and a zinc-nickel alloy plated layer. More specifically, the present invention relates to a copper foil for printed circuit and a copper-clad laminate capable of inhibiting the penetration of the etching solution into the base of the circuit when performing soft etching after forming the circuit. The copper foil of the present invention can be suitably applied, for example, to a fine pattern printed circuit and a magnetic head FPC (Flexible Printed Circuit).
Copper and copper alloy foil (hereinafter collectively referred to as “copper foil”) has contributed significantly to the development of the electric/electronic industry and, in particular, is indispensible as a printed circuit material. A copper foil for printed circuit is generally prepared as follows. Specifically, copper foil is adhesively laminated to a base material such as a synthetic resin board or film using an adhesive or without using an adhesive under high temperature and pressure in order to produce a copper-clad laminate; and, in order to subsequently form the intended circuit, etching treatment is performed for eliminating the unwanted parts after the required circuit is printed via the processes of photoresist application and exposure.
Ultimately, the required element is soldered to form various types of printed-circuit boards for electronic devices. The quality demand for a copper foil for printed-circuit board differs between the surface (roughened surface) adherent to the resin base material and the nonadherent surface (glossy surface), and numerous methods have been proposed for both.
For example, main requirements of the roughened surface are as follows: (1) no oxidative discoloration during the storage thereof, (2) sufficient peeling intensity with the base material even after high-temperature heating, wet processing, soldering, chemical treatment and the like, and (3) no so-called stacking fault occurred after the lamination with the base material and etching.
Roughening treatment plays an important role in deciding the adhesiveness between the copper foil and the base material. As the roughening treatment, the copper roughening treatment of electrodepositing copper was initially adopted, but various other technologies have been proposed thereafter, and in particular copper-nickel roughening treatment has become one of the representative treatment methods for improving the thermal peeling strength, hydrochloric acid resistance and oxidation resistance.
The present applicant has proposed the copper-nickel roughening treatment (refer to Patent Document 1), and achieved results. The copper-nickel treated surface takes on a black color and, in particular, with a rolled foil for flexible substrate, the black color resulting from the copper-nickel treatment is acknowledged as the symbol of the product.
Nevertheless, while the copper-nickel roughening treatment is superior in terms of thermal peeling strength, oxidation resistance and hydrochloric acid resistance, it is difficult to perform etching with an alkali etching solution which is becoming important for fine pattern treatment in recent years, and the treated layer becomes etching residue during the formation of such a fine pattern that the circuit line width is 150 μm pitches or less.
Thus, as a fine pattern treatment method, the present application has previously developed the Cu—Co treatment (refer to Patent Document 2 and Patent Document 3) and the Cu—Co—Ni treatment (refer to Patent Document 4). These roughening treatments yield favorable etching properties, alkali etching properties and hydrochloric acid resistance, but it was once again discovered that the thermal peeling strength would deteriorate when an acrylic adhesive is used, the oxidation resistance was also insufficient, and the color was brown to umber brown and does not reach black.
Pursuant to the trend of finer patterns and diversification of printed circuits in recent years, the following are being demanded; namely, 1) to possess thermal peeling strength (particularly when using an acrylic adhesive) and hydrochloric acid resistance that are comparable to cases of performing Cu—Ni treatment, 2) to be able to etch a printed circuit having a circuit line width of 150 μm pitches or less with an alkali etching solution, 3) to improve the oxidation resistance (oxidation resistance in an oven at 180° C.×30 minutes) as in the case of Cu—Ni treatment, and 4) to achieve blackening treatment as in the case of Cu—Ni treatment.
In other words, the finer circuit develops a strong tendency of the circuit to peel off due to the hydrochloric acid etching solution, and it is necessary to prevent such peeling of the circuit. When the circuit becomes finer, the circuit tends to peel off due to high temperatures caused by soldering and other treatments, and it is also necessary to prevent such peeling of the circuit. In increasingly finer patters; for instance, it is an essential requirement to be able to etch a printed circuit having a circuit line width of 150 μm pitches or less with a CuCl2 etching solution, and alkali etching is also becoming an essential requirement pursuant to the diversification of the photoresist and the like. A black surface is also becoming important for the manufacture of copper foils and from the perspective of chip mounts in order to improve the positioning accuracy and thermal absorption.
In response to the foregoing demands, the present applicant succeeded in developing a copper foil treatment method in order to obtain, as a result of performing roughening treatment on the surface of the copper foil by way of copper-cobalt-nickel alloy plating and thereafter forming a cobalt plated layer or a cobalt-nickel alloy plated layer, a copper foil for printed circuit that: comprises many of the general characteristics described above, particularly the various characteristics described above as in the case of Cu—Ni treatment; does not reduce the thermal peeling strength even when using an acrylic adhesive; and has superior oxidation resistance and a surface color that is black (refer to Patent Document 5).
Preferably, after forming the cobalt plated layer or the cobalt-nickel alloy plated layer, rust-proof treatment as represented with a single coating (metal coating) of chrome oxide or a composite coating (alloy coating) of chrome oxide, and zinc and/or zinc oxide is performed.
Subsequently, with the development of electronic equipment, the miniaturization and high integration of semiconductor devices advanced even further. Accordingly, the adhesive strength between the copper foil and the resin base material decreases because the treatments performed during the manufacture of these printed circuits are based on even higher temperatures and heat is generated during the use of devices after productization, and it has been a problem.
In light of the above, in the treatment method of a copper foil for printed circuit established in Patent Document 5 in which roughening treatment is performed to the surface of a copper foil by way of copper-cobalt-nickel alloy plating and thereafter a cobalt plated layer or a cobalt-nickel alloy plated layer is formed; the present applicant devised an invention for further improving the thermal peeling resistance when forming a cobalt-nickel alloy plated layer having better thermal deterioration resistance than a cobalt plated layer after the roughening treatment.
This is a treatment method of a copper foil for printed circuit, in which a cobalt-nickel alloy plated layer is formed after a roughening treatment on the surface of a copper foil by way of copper-cobalt-nickel alloy plating, and additionally a zinc-nickel alloy plated layer is formed. This is an extremely effective invention and is one of the major products of present-day copper foil circuit materials.
The present invention is a further improvement of the foregoing copper foil circuit material. A copper foil circuit is becoming even finer as described above, and the process of soft etching using an etching solution containing sulfuric acid and hydrogen peroxide on the surface of copper circuit after once forming the circuit on the substrate is being performed. During this process, a problem of penetration of the etching solution into the edge part of the adhesive site between a resin substrate of polyimide or the like and copper foil has occurred.
To put it differently, a part of the treatment surface of the copper foil is being corroded. This kind of corrosion will deteriorate the adhesive strength between the copper foil and the resin in a fine circuit, and is a major problem. Thus, a solution to this problem is required.    [Patent Document 1] Publication of Japanese Unexamined Patent Application No. S52-145769    [Patent Document 2] Publication of Japanese Examined Patent Application No. S63-2158    [Patent Document 3] Japanese Patent Application No. H1-112227    [Patent Document 4] Japanese Patent Application No. H1-112226    [Patent Document 5] Publication of Japanese Examined Patent Application No. H6-54831    [Patent Document 6] Japanese Patent No. 2849059